1. Field of the Invention
The present invention relates in general to a voltage regulator apparatus and, in particular, to a low-drop out voltage regulator apparatus with a sharp shut-off characteristic.
2. Background Art
Voltage regulators are well known in the art. Three-terminal voltage regulators accept an input voltage to produce a regulated output voltage which is held constant, as compared to ground, even during variation in the load. There are many different types of voltage regulators, for instance, there are low-power and low-dropout regulators. The term low-power is self-explanatory. Low-dropout regulators are voltage regulators which require less "headroom" than standard regulators. "Headroom" is the voltage measure required between unregulated and regulated voltage for operation, which for a standard regulator is 2 volts (or 3 base-emitter voltage drops). Low-dropout voltage regulators require approximately a half-volt headroom. Thus, low-dropout regulators are particularly useful in applications where rechargeable batteries are used. However, some of these regulators pull excessive quiescent current as they fall out of regulation. This excessive current draw causes a rechargeable battery to be deeply discharged--a highly undesirable condition.
It is thus an object of the present invention to provide a low-dropout voltage regulator which has a sharp cutoff as it begins to fall out of regulation, so as to prevent pulling an excessive quiescent current.
This and other objects will be become apparent in light of the attached specification and drawings.